Re: Battery switch location
I don't know if easy access is as important as proximity to the batteries. At most you switch the thing when starting up/shutting down for the day (or the weekend), or possibly midway through a trip to split the load. Having the thing behind a hatch isn't a big deal. Cable diameter goes up seriously if there is a long way to the switch, and it's a lot easier to maintain and diagnose any problems with the setup if everything is in one place.
I do agree that having it outside is not a great idea.